1. Field of the Invention
The present invention relates to a large-sized single- or multiple-screw resin material extruder having a gear pump at the leading end of a cylinder having built-in screws, wherein the direction of the flow passage of the gear pump is set perpendicular to the direction of the flow passage of the cylinder.
2. Related Art
FIG. 7 and 8 are a top and a side view of a conventional resin material extruder in which the direction of the flow passage of a gear pump is set perpendicular to that of the flow passage of a cylinder.
More specifically, the upstream end portion of a cylinder 2 having built-in screws is coupled to a speed reducer 1 to which a motor 5 is coupled and a gear pump 8 is coupled via a diverter valve 9 to the downstream, forward end of the cylinder 2 in a direction perpendicular to the flow passage of the cylinder 2. Further, a screen unit 7 and a granulating unit 6 are successively coupled to the gear pump 8. The speed reducer 1 is securely positioned.
The upstream end portion of the cylinder 2 is securely coupled to the speed reducer 1. The cylinder 2 is also movably supported with respective supports 4 at two places on both sides thereof in the longitudinal direction. The diverter valve 9 is securely coupled to the forward delivery opening of the cylinder 2.
The main discharge port of the diverter valve 9 is opened toward one side of the cylinder 2.
The gear pump 8, the screen unit 7 and the granulating unit 6 are coupled together successively and securely. The screen unit 7 is movably supported with respective supports 4' on both sides thereof in the direction of the flow passage, that is, in the direction perpendicular to the flow passage of the cylinder 2. The inhalation port of the gear pump 8 is securely coupled to the main discharge port of the diverter valve 9.
The inhalation port of the gear pump 8 and the main discharge port of the diverter valve 9 are coupled together under the cooling condition in such a way that, in consideration of the thermal expansion of the cylinder 2 at the time of normal operation of the extruder, the main discharge port of the diverter valve 9 is slightly shifted to the upstream side of the cylinder 2 to make it slidable and movable as the temperature of the cylinder 2 varies so as to make both the ports fit in with each other at the time of the normal operation during which the extruder is heated up to a set temperature.
The extruder thus constructed is first heated up to a predetermined temperature when it is operated. The extruder thus heated then kneads and melts the resin material supplied into the cylinder 2 having the rotatable screws. The molten resin material is pressurized by the gear pump 8 via the diverter valve 9 and delivered via the screen unit 7 into the granulating unit 6 where the molten resin material is granulated and solidified.
When the cylinder 2 is heated up, its total length becomes greater than that in cold condition as it elongates because of thermal expansion. However, the elongation totally appears in the downstream, forward end portion of the cylinder 2 since the upstream end portion thereof is securely coupled to the speed reducer 1 which is also securely disposed. The cylinder 2 thus elongates in the direction of its downstream, forward end portion.
As a result, the main discharge port of the diverter valve 9 which has shifted from the inhalation port of the gear pump 8 in cold condition fits the latter, so that the normal fluidity of the molten resin material is obtained.
The diverter valve 9 is equipped with a sub-discharge port for discharging the molten resin material outside when it is found inferior or unstable in quality at the outset of the operation of the extruder, for example, and used to switch the main discharge port to the sub-discharge port and vice versa as occasion demands.
The screen unit 7 separates alien substances by filtering the molten resin material.
However, the joint between the main discharge port of the diverter valve 9 and the inhalation port of the gear pump 8 is hardly sealed up even if a seal member is used because the former is fitted to the latter slidably and movably. Consequently, the molten resin material flowing inside may leak out through the joint. Moreover, the elongation of the cylinder changes from time to time as the heat-up temperature of the cylinder varies with the resin material, the operating condition and the like, and as the temperature of the cylinder also varies with the atmospheric temperature.
Therefore, the main discharge port of the diverter valve 9 needs to be always slidably coupled to the inhalation port of the gear pump 8 at the joint. In other words, the joint is hard to be locked securely and tightly after the cylinder is heated up.
If the joint is locked securely and tightly after the cylinder is heated up, the equipment may be gouged out at the joint as the elongation of the cylinder varies and the arrangement of the equipment may be badly affected thereby. A gap, if produced, at the joint may also cause the molten resin material to leak out.
As the temperature of the cylinder varies, moreover, the elongation of the cylinder rarely agrees to what has been estimated and it is often the case with the diverter valve whose main discharge port falls in discord with the inhalation port of the gear pump.
The molten resin material tends to collect in such a discordant spot and what has stayed thereat for hours becomes inferior in quality, thus causing the quality of granulated resin products to be deteriorated as the molten resin material inferior in quality is allowed to mix up.